Organic electroluminescent device having thin film encapsulation structure and method of fabricating the same

ABSTRACT

Provided is an organic electroluminescent display device, including a substrate, an organic light-emitting device on the substrate, and an encapsulation layer formed on the organic light-emitting device and the substrate. The encapsulation layer includes an inorganic layer and a polymer organic layer alternatingly stacked with an intermediate layer formed of a first organic monomer between the inorganic layer and the polymer organic layer, and one surface of the intermediate layer is bonded to the inorganic layer through bonding sites on a surface of the inorganic layer and another surface of the intermediate layer is bonded to the organic layer by polymerization.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/646,583, filed Dec. 30, 2021, which is a continuation of U.S. patentapplication Ser. No. 17/170,721, filed Feb. 8, 2021, now U.S. Pat. No.11,245,098, which is a continuation of U.S. patent application Ser. No.16/837,353, filed Apr. 1, 2020, now U.S. Pat. No. 10,944,076, which is acontinuation of U.S. patent application Ser. No. 16/389,696, filed Apr.19, 2019, now U.S. Pat. No. 10,644,264, which is a continuation of U.S.patent application Ser. No. 16/188,133, filed Nov. 12, 2018, now U.S.Pat. No. 10,297,791, which is a continuation of U.S. patent applicationSer. No. 15/725,150, filed Oct. 4, 2017, now U.S. Pat. No. 10,128,464,which is a continuation of U.S. patent application Ser. No. 15/155,260,filed May 16, 2016, now U.S. Pat. No. 9,831,468, which is acontinuation-in-part of U.S. patent application Ser. No. 14/059,187,filed Oct. 21, 2013, now U.S. Pat. No. 9,373,813, which claims priorityto and the benefit of Korean Patent Application No. 10-2013-0016057,filed Feb. 14, 2013, the entire contents of all of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention generally relates to an organic electroluminescentdevice having a thin film encapsulation structure, and moreparticularly, to an organic electroluminescent device having a thin filmencapsulation structure, in which an inorganic layer and an organiclayer are stacked, and a method of fabricating the same.

2. Description of the Related Art

Encapsulation technology of an organic light-emitting device may includesubstrate bonding technology for bonding an encapsulation substrate anda substrate having an organic light-emitting device formed thereon toeach other, and a thin film encapsulation technology for forming anencapsulation layer in the form of a thin film without an encapsulationsubstrate. The bonding of the encapsulation substrate and the substratehaving an organic light-emitting device formed thereon is performed byusing an inorganic frit or an organic adhesive. An inorganic layer, suchas AlOx, SiNx, SiOx, and SiON, on a panel may be used for thin filmencapsulation.

An inorganic layer for thin film encapsulation is thin, but a densitythereof is high, and thus, the inorganic layer for thin filmencapsulation may have barrier characteristics with respect to moistureand oxygen. However, since an inorganic layer has brittlecharacteristics, mechanical properties thereof under stress may be poor.In particular, a plurality of particles may exist on a substrate duringa process of fabricating an organic light-emitting device, and aninorganic layer disposed on the particles may be significantly affectedby stress, and thus, the barrier characteristics of the inorganic layermay be degraded.

Therefore, a structure is introduced for planarizing an irregularsurface, such as particles, by introducing an organic layer between theinorganic layers as well as relieving the stress of the inorganic layer.Acryl, silicone, and epoxy are used as the organic layer.

In general, thermal stability must be maintained at about 100° C. forthe reliability of the organic light-emitting device. However, aphenomenon of peeling-off of an interface between the inorganic layerand the organic layer may occur during exposure at a high temperaturefor a prolonged period of time. For example, since strong chemicalbonding may be difficult to be formed in the case where an acryl layeris deposited on a SiNx layer deposited through a plasma enhancedchemical vapor deposition (PECVD) process, an interface between the SiNxlayer and the acryl layer may be peeled off due to heat.

SUMMARY

The present invention provides an organic light-emitting device having astable thin film encapsulation structure by improving interfacialadhesion between an inorganic layer and an organic layer, and a methodof fabricating the same.

According to an aspect of the present invention, there is provided anorganic electroluminescent display device including a substrate, anorganic light-emitting device on the substrate, and an encapsulationlayer formed on the organic light-emitting device and the substrate. Theencapsulation layer includes an inorganic layer and a polymer organiclayer alternatingly stacked with an intermediate layer formed of a firstorganic monomer between the inorganic layer and the polymer organiclayer, and one surface of the intermediate layer is bonded to theinorganic layer through bonding sites on a surface of the inorganiclayer and another surface of the intermediate layer is bonded to theorganic layer by polymerization.

According to another aspect of the present invention, there is provideda method of fabricating an organic electroluminescent display deviceincluding providing a substrate, forming an organic light-emittingdevice on the substrate, and forming an encapsulation layer including aninorganic layer and a polymer organic layer alternatingly stacked withan intermediate layer formed of a first organic monomer between theinorganic layer and the polymer organic layer on the organiclight-emitting device and the substrate. One surface of the intermediatelayer is bonded to the inorganic layer through bonding sites on asurface of the inorganic layer and another surface of the intermediatelayer is bonded to the organic layer by polymerization.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a cross-sectional view schematically illustrating an organicelectroluminescent display device constructed as an embodiment accordingto the principles of the present invention;

FIG. 2 is a cross-sectional view schematically illustrating an organicelectroluminescent display device 100 constructed as another embodimentaccording to the principles of the present invention; and

FIG. 3 is a diagram conceptually illustrating a process in which anintermediate layer forms a bond between an inorganic layer and anorganic layer.

DETAILED DESCRIPTION

Hereinafter, the present invention will be described more fully withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. The invention may, however, be embodied inmany different forms and should not be construed as being limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the concept of the invention to those of ordinary skill in theart. In the drawings, the thicknesses of layers and regions areexaggerated for clarity. Like reference numerals refer to like elementsthroughout.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items. Expressions such as “atleast one of,” when preceding a list of elements, modify the entire listof elements and do not modify the individual elements of the list.

FIG. 1 is a cross-sectional view schematically illustrating an organicelectroluminescent display device constructed as an embodiment accordingto the principles of the present invention.

An organic electroluminescent display device 100 constructed as anembodiment according to the principles of the present invention includesa substrate 10, an organic light-emitting device 20 on the substrate 10,and an encapsulation layer 30 formed on the substrate 10 to cover theorganic light-emitting device 20.

Substrates formed of various materials, such as glass, plastic, silicon,or metal, may be used as the substrate 10. A buffer layer (not shown)for preventing diffusion of impurity elements or ions and infiltrationof moisture from the substrate 10 to a thin film transistor (TFT) or theorganic light-emitting device 20 on the substrate 10 and for planarizinga surface of the substrate 10 may be formed on a top surface of thesubstrate 10. Also, a TFT (not shown), as a circuit for driving theorganic light-emitting device 20, is formed on the substrate 10.

The organic light-emitting device 20 includes a first electrode 21, asecond electrode 23, and an organic layer 22 between the first electrode21 and the second electrode 23.

The first electrode 21 may be an anode, and in this case, the firstelectrode 21 may be selected from materials having a high work functionso as to facilitate hole injection. The first electrode 21 may be atransmissive electrode or a reflective electrode. The first electrode21, for example, may be formed of indium tin oxide (ITO), indium zincoxide (IZO), zinc oxide (ZnO), aluminum (AD-doped zinc oxide (AZO),indium oxide (In₂O₃), or tin oxide (SnO₂). The first electrode 21 mayalso be formed as a reflective electrode by using magnesium (Mg), silver(Ag), Al, aluminum-lithium (Al—Li), calcium (Ca), Ag-ITO, Mg—In, orMg—Ag. The first electrode 21 may have a single layer structure or amultilayer structure having two or more layers. For example, the firstelectrode 21 may have a three-layer structure of ITO/Ag/ITO, but thefirst electrode 21 is not limited thereto.

The organic layer 22 in the organic light-emitting device 20 includes atleast an emissive layer (EML) and in addition, may further includelayers for hole injection and transport, electron injection andtransport, and charge balance.

The second electrode 23 may be a cathode, and in this case, a metal, analloy, an electrically conductive compound, or a mixture of two or morethereof having a low work function may be used as the second electrode23. The second electrode 23, for example, may be included as atransparent electrode or a reflective electrode. In the case that thesecond electrode 23 is included as a transparent electrode, the secondelectrode 23 may include a thin film formed of Li, Ca, Al, Mg, Mg—In,Mg—Ag, LiF—Al, LiF—Ca, or a compound thereof and an auxiliary electrodeformed of a transparent conductive material, such as ITO, IZO, ZnO, orIn₂O₃, disposed thereon. Alternatively, in the case that the secondelectrode 23 is included as a reflective electrode, the second electrode23 may be formed of Li, Ca, Al, Mg, Mg—In, Mg—Ag, LiF—Al, LiF—Ca, or acompound thereof.

The encapsulation layer 30 is composed of an inorganic layer 31 and anorganic layer 33 alternatingly stacked with an intermediate layer 32between the inorganic layer 31 and the organic layer 33.

The inorganic layer 31, for example, may be formed of silicon oxide,silicon nitride, silicon oxynitride, aluminum oxide, aluminum nitride,aluminum oxynitride, titanium oxide, titanium nitride, tantalum oxide,tantalum nitride, hafnium oxide, hafnium nitride, zirconium oxide,zirconium nitride, cerium oxide, cerium nitride, tin oxide, tin nitride,magnesium oxide, or hexamethyldisiloxane (HMDSO). An optimum thicknessof the inorganic layer 31 may be determined according to productivity ordevice characteristics. The inorganic layer 31 is thin, but a densitythereof is high, and thus, the inorganic layer 31 may have barriercharacteristics with respect to moisture and oxygen.

The organic layer 33 may be formed of an acryl-based resin, amethacryl-based resin, an isoprene-based resin, a vinyl-based resin, anepoxy-based resin, a urethane-based resin, a cellulose-based resin, aperylene-based resin, an imide-based resin, or a mixture of two or morethereof. For example, the organic layer 33 may be formed to include thesecond organic monomer which may comprise hexamethyldisiloxane (HMDSO);a monomer of an acryl-based resin, a methacryl-based resin, anisoprene-based resin, a vinyl-based resin, an epoxy-based resin, aurethane-based resin, a cellulose-based resin, a perylene-based resinand an imide-based resin. An optimum thickness of the organic layer 33may be determined according to characteristics of the inorganic layer31, productivity, and device characteristics. The organic layer 33 mayact to relieve stress of the inorganic layer 31 and planarize theinorganic layer 31.

One surface of the intermediate layer 32 is bonded to the inorganiclayer 31 through bonding sites on a surface of the inorganic layer 31,and another surface of the intermediate layer 32 is bonded to theorganic layer 33 by polymerization. The intermediate layer 32 may beformed of a material which may be bonded to a bonding site, such asoxygen, on the surface of the inorganic layer 31 and may be bonded tothe organic layer 33 by polymerization. The intermediate layer 32 may beformed of a first organic monomer which is an organic compound includinga polymerizable double bond. For example, the first organic monomercomprises methacrylate, acrylate, or epoxy. For example, a hydroxyl orcarbonyl moiety of methacrylate may be bonded to a bonding site, e.g.,an oxygen or hydrogen atom, on the surface of the inorganic layer 31and/or a carbonyl or carbon-carbon double bond moiety thereof may bebonded to the organic layer 33 by polymerization. An optimum thicknessof the intermediate layer 32 may be determined according to a degree ofadhesion between the inorganic layer 31 and the organic layer 33. Forexample, the intermediate layer 32 may be formed to a thickness of a fewtens of angstrom (Å), but the thickness of the intermediate layer 32 isnot limited thereto.

In the encapsulation layer 30, the pluralities of organic layers 33 andinorganic layers 31 may be alternatingly stacked and the intermediatelayer 32 may be disposed between the organic layer 33 and the inorganiclayer 31.

Since the intermediate layer 32 is bonded to the organic layer 33 andthe inorganic layer 31, adhesion between the organic layer 33 and theinorganic layer 31 is improved, and thus, occurrence of peeling-off dueto thermal stress and deformation may be prevented.

Hereinafter, a method of fabricating an organic electroluminescentdisplay device according to an embodiment of the present invention willbe described.

First, a substrate 10 is provided. Substrates formed of variousmaterials, such as glass, plastic, silicon, or metal, may be used as thesubstrate 10. A buffer layer (not shown) for preventing diffusion ofimpurity elements or ions and infiltration of moisture from thesubstrate 10 to a TFT or an organic light-emitting device 20 above thesubstrate 10 and for planarizing a surface of the substrate 10 may beformed on a top surface of the substrate 10. Also, a TFT (not shown), asa circuit for driving the organic light-emitting device 20, is formed onthe substrate 10.

The organic light-emitting device 20 electrically connected to the TFT(not shown) is formed on the substrate 10. The organic light-emittingdevice 20 includes a first electrode 21, a second electrode 23, and anorganic layer 22 between the first electrode 21 and the second electrode23.

The first electrode 21 may be an anode, and in this case, the firstelectrode 21 may be formed by selecting a material having a high workfunction so as to facilitate hole injection. The first electrode 21 maybe a transmissive electrode or a reflective electrode. The firstelectrode 21, for example, may be formed of ITO, IZO, ZnO, AZO, In₂O₃,or SnO₂. The first electrode 21 may also be formed as a reflectiveelectrode by using Mg, Ag, Al, Al—Li, Ca, Ag-ITO, Mg—In, or Mg—Ag. Thefirst electrode 21 may be formed as a single layer structure or amultilayer structure having two or more layers. The first electrode 21may be formed by evaporation or sputtering.

The organic layer 22 includes at least an EML and in addition, mayfurther include a hole injection layer (HIL), a hole transport layer(HTL), an electron transport layer (ETL), and an electron injectionlayer (EIL). The organic layer 22 may be formed of a low molecularweight or high molecular weight material, and may be formed by usingvarious methods, such as a vacuum deposition method, a spin coatingmethod, a casting method, and a Langmuir-Blodgett (LB) method.

The hole injection layer may be formed of a phthalocyanine compound,such as copper phthalocyanine,N,N′-diphenyl-N,N′-bis-[4-(phenyl-m-tolyl-amino)-phenyl]-biphenyl-4,4′-diamine(DNTPD), 4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine(m-MTDATA), 4,4′,4″-Tris(N,N-diphenylamino)triphenylamine (TDATA),4,4′,4″-tris{N,-(2-naphthyl)-N-phenylamino}-triphenylamine (2T-NATA),poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS),polyaniline/dodecylbenzenesulfonic acid (PANI/DBSA), polyaniline/camphorsulfonic acid (PANI/CSA), or polyaniline/poly(4-styrenesulfonate)(PANI/PSS). However, the hole injection layer is not limited thereto.

The hole transport layer may be formed of a carbazole derivative, suchas N-phenylcarbazole and polyvinylcarbazole, and a triphenylamine-basedmaterial such asN,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1-biphenyl]-4,4′-diamine(TPD), N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine (NPB), or4,4′,4″-tris(N-carbazolyl)triphenylamine (TCTA). However, the holetransport layer is not limited thereto.

The electron transport layer may be formed of Alq₃,2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP),4,7-diphenyl-1,10-phenanthroline (Bphen),3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole (TAZ),4-(Naphthalen-1-yl)-3,5-diphenyl-4H-1,2,4-triazole (NTAZ),2-(4-Biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (tBu-PBD),Bis(2-methyl-8-quinolinolato-N1,O8)-(1,1′-Biphenyl-4-olato)aluminum(BAlq), beryllium bis(benzoquinolin-10-olate) (Bebq₂), or9,10-di(naphthalene-2-yl)anthracene (ADN). However, the electrontransport layer is not limited thereto.

The electron injection layer may be formed by using a material such asLiF, NaCl, CsF, Li₂O, BaO, and Liq.

The emissive layer may be formed to include a host material and a dopantmaterial.

Examples of the host may be tris-(8-quinolinolato)aluminum (Alq₃),4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP), poly(n-vinylcabazole) (PVK),ADN, TCTA, 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBI),3-tert-butyl-9,10-di(naphtha-2-yl)anthracene (TBADN), distyrylarylene(DSA), E3, or 4,4′-bis(9-carbazolyl)-2,2′-dimethyl-biphenyl (CDBP).However, the host is not limited thereto.

Examples of the dopant may be Pt(II) octaethylporphine (PtOEP),tris(2-phenylisoquinoline)iridium (Ir(piq)₃),bis(2-(2′-benzothienyl)-pyridinato-N,C3′)iridium(acetylacetonate)(Btp₂Ir(acac)), tris(2-phenylpyridine)iridium (Ir(ppy)₃),Bis(2-phenylpyridine)(Acetylacetonato)iridium(III) (Ir(ppy)₂(acac)),tris(2-(4-tolyl)phenylpyridine)iridium (Ir(mppy)₃),10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-[1]benzopyrano[6,7,8-ij]quinolizin-11-one(C545T), Bis[3,5-difluoro-2-(2-pyridyl)phenyl](picolinato)iridium(III)(F₂Irpic), (F₂ppy)₂Ir(tmd), Ir(dfppz)₃,4,4′-bis(2,2′-diphenylethen-1-yl)biphenyl (DPVBi),4,4′-bis[4-(diphenylamino)styryl]biphenyl (DPAVBi), or2,5,8,11-tetra-tert-butyl perylene (TBPe). However, the dopant is notlimited thereto.

The second electrode 23 may be a cathode, and in this case, the secondelectrode 23 may be formed by using a metal, an alloy, an electricallyconductive compound, or a mixture of two or more thereof having a lowwork function. The second electrode 23, for example, may be formed as atransparent electrode or a reflective electrode. In the case that thesecond electrode 23 is a transparent electrode, the second electrode 23may be formed as a thin film formed of Li, Ca, Al, Mg, Mg—In, Mg—Ag,LiF—Al, LiF—Ca, or a compound thereof and an auxiliary electrode formedof a transparent conductive material, such as ITO, IZO, ZnO, or In₂O₃,disposed thereon. Alternatively, in the case where the second electrode23 is a reflective electrode, the second electrode 23, for example, maybe formed of Li, Ca, Al, Mg, Mg—In, Mg—Ag, LiF—Al, LiF—Ca, or a compoundthereof. The second electrode 23 may be formed by sputtering or vacuumdeposition.

An encapsulation layer 30 is formed on the organic light-emitting device20.

The encapsulation layer 30 is composed of an inorganic layer 31 and anorganic layer 33 alternatingly stacked with an intermediate layer 32between the inorganic layer 31 and the organic layer 33.

The inorganic layer 31, for example, may be formed of silicon oxide,silicon nitride, silicon oxynitride, aluminum oxide, aluminum nitride,aluminum oxynitride, titanium oxide, titanium nitride, tantalum oxide,tantalum nitride, hafnium oxide, hafnium nitride, zirconium oxide,zirconium nitride, cerium oxide, cerium nitride, tin oxide, tin nitride,or magnesium oxide. An optimum thickness of the inorganic layer 31 maybe determined according to productivity or device characteristics. Theinorganic layer 31 may be formed by using a method such as chemicalvapor deposition (CVD), plasma enhanced chemical vapor deposition(PECVD), sputtering, atomic layer deposition (ALD), or thermalevaporation.

Bonding sites to be bonded to the intermediate layer 32 are formed onthe surface of the inorganic layer 31. The bonding sites, for example,may be an oxygen atomic layer. For this purpose, the surface of theinorganic layer 31 may be treated with oxygen plasma or ozone plasma. AnM-H bond on the surface of the inorganic layer 31 may be changed to anM-OH bond by such an oxygen or ozone plasma treatment, where M denotessilicon or metal elements of the inorganic layer 31, such as silicon,aluminum, titanium, tantalum, hafnium, zirconium, cerium, tin, ormagnesium.

A preliminary intermediate layer (not shown) is formed on thesurface-treated inorganic layer 31 by using a first organic monomerhaving a polymerizable double bond, such as a vinyl group or a carbonylgroup, and a photopolymerization initiator. For example, the preliminaryintermediate layer (not shown) may be formed of the first organicmonomer comprising methacrylate, acrylate, or epoxy. Examples of thephotopolymerization initiator may be an acetophenone-based compound, abenzophenone-based compound, a thioxanthone-based compound, abenzoin-based compound, and a triazine-based compound. However, thepreliminary intermediate layer is not limited thereto. The abovematerials may be used alone or by mixing two or more thereof.

The preliminary intermediate layer (not shown) may be formed by using aflash evaporation method, an inkjet process, a screen printing method, aspin coating method, or an initiated chemical vapor deposition (iCVD)method forming vapor phase radicals at high temperatures. Thepreliminary intermediate layer (not shown) may be formed to a thicknessof a few tens of angstrom (Å), but the thickness of the preliminaryintermediate layer is not limited thereto. The organic monomer of thepreliminary intermediate layer (not shown) may be bonded to the bondingsites of the inorganic layer 31.

Next, a preliminary organic layer (not shown) may be formed on thepreliminary intermediate layer (not shown) by using a second organicmonomer. The preliminary organic layer (not shown), for example, may beformed of an acryl-based resin, a methacryl-based resin, anisoprene-based resin, a vinyl-based resin, an epoxy-based resin, aurethane-based resin, a cellulose-based resin, a perylene-based resin,an imide-based resin, or a mixture thereof. For example, the secondorganic monomer may comprise hexamethyldisiloxane (HMDSO); a monomer ofan acryl-based resin, a methacryl-based resin, an isoprene-based resin,a vinyl-based resin, an epoxy-based resin, a urethane-based resin, acellulose-based resin, a perylene-based resin and an imide-based resin.The preliminary organic layer (not shown), for example, may be formed byusing a method such as a flash evaporation method, an inkjet process, ascreen printing method, or a spin coating method.

Subsequently, the preliminary intermediate layer (not shown) and thepreliminary organic layer (not shown) are cured by using ultraviolet(UV) or heat. A vinyl group of the first organic monomer of thepreliminary intermediate layer (not shown) is polymerized with thesecond organic monomer of the preliminary organic layer (not shown), andthe second organic monomer of the preliminary organic layer (not shown)is polymerized with the first organic monomer of the preliminaryintermediate layer (not shown) and another monomer of an organic layer(not shown). After a curing process, the preliminary intermediate layer(not shown) becomes the intermediate layer 32 and the preliminaryorganic layer (not shown) becomes the organic layer 33. Thus, theintermediate layer 32 is bonded to the organic layer 33 according tosuch polymerizations and the organic layer 33 forms a resin layer or apolymer layer.

FIG. 2 is a cross-sectional view schematically illustrating an organicelectroluminescent display device 100 constructed as another embodimentaccording to the principles of the present invention. In FIG. 2 ,descriptions of substrate 10, an organic light-emitting device 20, afirst electrode 21, an organic layer 22, a second electrode 23, anencapsulation layer 30, an inorganic layer 31, intermediate layer 32 andan an organic layer 33 may be understood by referring to thedescriptions provided herein.

FIG. 3 is a diagram conceptually illustrating a process, in which anintermediate layer forms a bond between an inorganic layer and anorganic layer, according to an embodiment of the present invention.

Referring to FIG. 3 , in step S1, the inorganic layer having a —H bondon a surface of the inorganic layer is prepared.

Then in step S2, the —H bond on the surface of the inorganic layer ischanged to a —OH bond by a surface treatment.

In step S3, a preliminary intermediate layer, in which a part R₁ isbonded to O of the inorganic layer and a vinyl group faces a surface, isformed on the surface-treated inorganic layer by using R₁═CH₂, anorganic monomer having a vinyl group.

Next, in step S4, a preliminary organic layer is formed by using anorganic monomer R₂; and then the organic monomer R₂ and the vinyl groupof the preliminary intermediate layer are polymerized by curing to forma bond.

The intermediate layer thus is bonded to the organic layer and theinorganic layer, and as a result, adhesion between the organic layer andthe inorganic layer is improved. Therefore, occurrence of peeling-offdue to thermal stress may be prevented. Meanwhile, the bonding sites onthe surface of the inorganic layer are not limited to only —OH and thepolymerizable group of the organic monomer of the preliminaryintermediate layer is not limited to only a vinyl group.

Since an intermediate layer is bonded to an organic layer and aninorganic layer, adhesion between the organic layer and the inorganiclayer are improved, and thus, occurrence of peeling-off due to thermalstress may be prevented.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

What is claimed is:
 1. A display device, comprising: a substrate; a light-emitting device on the substrate; and an encapsulation layer on the light-emitting device and the substrate, wherein the encapsulation layer comprises a first inorganic layer, and a second inorganic layer, wherein the first inorganic layer is the closest layer of the encapsulation layer to the substrate, wherein the second inorganic layer comprises a third region and a fourth region, wherein the third region is between the first inorganic layer and the fourth region, and a concentration of oxygen in the third region is greater than a concentration of oxygen in the fourth region.
 2. The display device of claim 1, wherein the third region has a portion having a maximum oxygen concentration in the second inorganic layer.
 3. The display device of claim 1, wherein the second inorganic layer comprises silicon oxide, silicon nitride, silicon oxynitride, aluminum oxide, aluminum nitride, aluminum oxynitride, titanium oxide, titanium nitride, tantalum oxide, tantalum nitride, hafnium oxide, hafnium nitride, zirconium oxide, zirconium nitride, cerium oxide, cerium nitride, tin oxide, tin nitride, magnesium oxide or hexamethyldisiloxane (HMDSO).
 4. The display device of claim 1, wherein the second inorganic layer comprises silicon nitride, aluminum nitride, titanium nitride, tantalum nitride, hafnium nitride, zirconium nitride, cerium nitride, or tin nitride.
 5. The display device of claim 1, wherein the light-emitting device comprises an organic light-emitting device comprising a first electrode, a second electrode, and an organic emissive layer between the first electrode and the second electrode.
 6. The display device of claim 5, wherein the organic light-emitting device further comprises at least one of a hole injection layer, a hole transport layer, an electron injection layer, or an electron transport layer between the first electrode and the second electrode.
 7. The display device of claim 1, wherein the encapsulation layer further comprises a polymer layer between the first inorganic layer and the second inorganic layer, wherein the second inorganic layer of the encapsulation layer contacts the polymer layer.
 8. The display device of claim 7, wherein the polymer layer is derived from a first organic monomer comprising methacrylate, acrylate, or epoxy.
 9. The display device of claim 7, wherein one surface of the polymer layer is in contact with the first inorganic layer, wherein the inorganic layer comprises a first region and a second region between the first region and the polymer layer, and a concentration of oxygen in the second region is greater than a concentration of oxygen in the first region.
 10. The display device of claim 9, wherein the second region has a portion having a maximum oxygen concentration in the inorganic layer. 